Tran Thi Kim Chi

Time-resolved photoluminescence measurements of InP/ZnS quantum dots

This paper reports the results on the time-resolved photoluminescence study of InP/ZnS core/shell quantum dots. The ZnS shell played a decisive role to passivate imperfections on the surface of InP quantum dots, consequently giving rise to a strong enhancement of the photoluminescence from the InP core. Under appropriate excitation conditions, not only the emission from the InP core but also that from the ZnS shell was observed. The emission peak in InP core quantum dots varied as a function of quantum dots size, ranging in the 600 – 700 nm region; while the ZnS shell showed emission in the blue region around 470 nm, which is interpreted as resulting from defects in ZnS.

CdTe quantum dots for an application in the life sciences

This report highlights the results of the preparation of semiconductor CdTe quantum dots (QDs) in the aqueous phase. The small size of a few nm and a very high luminescence quantum yield exceeding 60% of these materials make them promisingly applicable to bio-medicine labeling. Their strong, two-photon excitation luminescence is also a good characteristic for biolabeling without interference with the cell fluorescence. The primary results for the pH-sensitive CdTe QDs are presented in that fluorescence of CdTe QDs was used as a proton sensor to detect proton flux driven by adenosine triphosphate (ATP) synthesis in chromatophores. In other words, these QDs could work as pH-sensitive detectors. Therefore, the system of CdTe QDs on chromatophores prepared from the cells of Rhodospirillum rubrum and the antibodies against the beta-subunit of F0F1–ATPase could be a sensitive detector for the avian influenza virus subtype A/H5N1.

Detection of the pesticide by functionalised quantum dots as fluorescence–based biosensor

In this paper, we present the new results of biosensor that is made from the surface–modified quantum dots with acetylcholinesterase enzymes (AChE) for optical detection of the pesticides. The quantum dots (QDs) mentioned in this study are CdTe, CdSe/ZnS and CdSe/ZnSe/ZnS - the thick shell QDs are totally new. The results pointed out that all of the quantum dots are fit for the role of transducers in biosensor. In the biosensor, the QD– streptavidine - AChE is used as the substrate for the detection of pesticide. The pesticides used in this work are Parathion Methyl (PM) and Acetamiprid. The acetylthiocholine (ATCh) is used as an indicator of the activity of the AChE enzyme. Alternatively, the organophosphorus (OP) pesticides are the inhibitor for the AChE enzymes. Therefore, the mixture of the pesticide and ATCh is used for the goal of the specification of pesticide. We can detect pesticides by the change in PL intensity of QDs biosensor, with the content ranges from 0.05 ppb to 10 ppb.

Synthesis and characterization of core/shell structured nanophosphors CePO4:Tb@LaPO4 by solvothermal method

Abstract Core/shell structured CePO4:Tb(III)@LaPO4 and CePO4:Tb(III) were successfully synthesized in tris(2–ethylhexyl) phosphate (TEHP) and diethylene glycol (DEG) solvents for comparison of the two techniques in open air and closed reaction vessel. Morphology and crystal structure of the core/shell nanophosphors were determined by using X-ray diffraction (XRD) and transmission electron microscopy (TEM), which showed that nanophosphors had diameter of about 5–10 nm with the monoclinic monazite phase. The nanophosphors obtained by close vessel procedure showed smaller size, more homogeneity and pure crystallite. The luminescent measurements were done upon the different excitation wavelengths in ultraviolet region and at room temperature to elucidate the influences of the used solvents and the reaction temperatures. It was found that CePO4:Tb@LaPO4 prepared by the close vessel synthesis showed the intensity of green band of the transfer from 5D4 to 7F5 energy level, which was strongly increased, and the luminescent decay time was 3.2 ms, which was longer than that of naked CePO4:Tb phosphor.

Enhanced Photocatalytic Activity of {110}-Faceted TiO2 Rutile Nanorods in the Photodegradation of Hazardous Pharmaceuticals

Rutile TiO2 with highly active facets has attracted much attention owing to its enhanced activity during the photocatalytic degradation of pollutants such as pharmaceuticals in wastewater. However, it is difficult to obtain by controlling the synthetic conditions. This paper reports a simple hydrothermal synthesis of rutile TiO2 nanorods with highly exposed {110} facets. The obtained rutile was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and Raman spectroscopy. The main contribution to the photocatalytic activity comes from rutile nanorods with highly dominant active {110} facets, which were studied in the photodegradation of reactive cinnamic acid and more recalcitrant ibuprofen. The contribution of active species was also investigated. The present work further confirmed the hydrothermal synthesis route for controlling the preparation of highly crystalline and active rutile nanocrystals.

Preparation of SERS Substrates for the Detection of Organic Molecules at Low Concentration

In this paper, we present the results of the preparation of Surface Enhanced Raman Spectroscopy (SERS) substrates by depositing silver nanoparticles (Ag NPs) onto a porous silicon wafer that is produced by the chemical etching process. The influences of the preparation parameters such as resistivity of the silicon wafer, the anodizing current density, etching time to the size of pores were systematically investigated. The SERS substrates prepared were characterised by using appropriate techniques: the morphology and pores size by scanning electron microscope (SEM), the SERS activity by Raman scattering measure of organic molecules malachite green (MG) embedded into the substrate at room temperature. Our experimental results show that a home-made Raman microscope system could be efficiently used to detect the MG molecules at the concentration lower than 10 -7 M with the prepared SERS substrates which have Ag NPs in the obtained pores of 10 – 40 nm.

Optical Detection of the Pesticide by Functionalized Quantum Dots as Fluorescence-Based Biosensor

In this work, the results on using biosensor composed from quantum dots as transducer and acetylcholinesterase enzymes (AChE) to detect pesticides optically are presented. The used quantum dots were CdTe, CdSe/ZnS 10 monolayer (ML) and CdSe/ZnSe2ML/ZnS 8 ML – the brand new thick-shell quantum dots (QD). The study results pointed out that the CdSe/ZnS 10 ML and CdSe/ZnSe 2ML/ZnS 8ML quantum dots best fit for the role of transducers in biosensors. In the biosensor, acetylthiocholine (ATCh) is used as indicator for the AChE enzymes to work, since it is a very powerful hydrolyte with the presence of AChE enzymes. Moreover, the organophosphorus (OP) pesticides are the inhibitors for the AChE enzymes, thus, by the biosensors that we designed, we can detect pesticides by the change in photoluminescence (PL) intensity of QDs, with the detection of OP like parathion methyl is 0.05 ppm, and acetamiprid is 2.5 ppm.

Novel Amorphous Molybdenum Selenide as an Efficient Catalyst for Hydrogen Evolution Reaction

Amorphous molybdenum selenide nanopowder, obtained by refluxing Mo(CO)6 and Se precursors in dichlorobenzene, shows several structural and electrochemical similarities to the amorphous molybdenum sulfide analogue. The molybdenum selenide displays attractive catalytic properties for the hydrogen evolution reaction in water over a wide range of pH. In a pH 0 solution, it operates with a small onset overpotential of 125 mV and requires an overpotential of 270 mV for generating a catalytic current of 10 mA/cm2. Compared with molybdenum sulfide, the selenide analogue is more robust in a basic electrolyte. Therefore, molybdenum selenide is a potential candidate for incorporating within an electrolyzer or a photoelectrochemical cell for water electrolysis in acidic, neutral, or alkaline medium.